Feature request

Feature description

We have implemented a ground contour algorithm in our perception pipeline. A field "height" is appended to the point cloud fields that contains the measurement of a given point height relative to the ground contour mesh. This allows us to more reliably consider object heights in operational design domains that are not flat. This is common for us in our application which is a hay or corn field.

I have hard coded changes to our own copied version of the collision monitor source code but it would be great if there was support for this in upstream nav2 to reduce maintenance effort on our side.

Implementation considerations

I would expect most users would continue to use the base x, y, and z fields so this would need to be something configurable in the parameters file. Also since our height field is already relative to a ground contour we skip the transform in the point iterator for that field, but still transform the x and y fields.

In total the proposed changes would consist of adding support for substituting custom fields and optionally not applying the transform operation to them.

I am working on merging the hard coded changes into a fork and will link it here for clarity once I have that done.